Through standard, this is not possible. While creating the return sale order, system should validate the Clearing Date (AUGDT) from BSEG table with FKDAT from VBRK and if it exceeds 9 months, then system should not allow to save the return order. For this, you can try with USEREXIT_CHECK_VBAK in program MV45AFZB
G. Lakshmipathi